390 DIGESTIVE SYSTEM OF THE HORSE 



of the petrous temporal bone and from the lateral lamina of the Eustachian tube, 

 and passes at first forward, lateral to the latter; it then inclines ventrally across 

 the deep face of the anterior pharyngeal muscles and turns medially into the soft 

 palate, in which it spreads out above the glandular layer. It raises the soft palate, 

 thus closing the posterior nares during deglutition. 



The tensor palati (M. tensor veU palatini) is larger than the levator, and is 

 fusiform and flattened. It arises from the muscular process of the petrous tem- 

 poral bone, the pterygoid bone, and the lateral lamina of the Eustachian tube, 

 and passes forward, lateral to the levator, across the medial surface of the origin of 

 the pterygoideus medialis. Its tendon is then reflected around the hainulus of the 

 pterygoid bone, where it is held in position by a flbrous band and lubricated by a 

 bursa, turns inward and expands in the aponeurosis of the soft palate. It tenses 

 the soft palate. 



Vessels and Nerves. — The blood-supply of the soft palate is derived from the 

 internal and external maxillary arteries and the blood is carried away by the corres- 

 ponding veins. The lymph vessels go to the pharyngeal lymph glands. The nerves 

 come from the trigeminus, vagus, and glosso-pharyngeal nerves. 



The floor of the mouth in its anterior part is free and is formed by the body of 

 the mandible, covered by mucous membrane. The remainder is occupied by the 

 attached portion of the tongue in the undisturbed state of the parts. The follow- 

 ing features are exposed by raising the tongue and drawing it to one side. About 

 opposite the canine tooth on each side is a papilla, the caruncula sublingualis, 

 through which the duct of the mandibular gland opens. Just behind these papillae 

 is a median fold of mucous membrane which passes to the ventral surface of the 

 tongue, constituting the frenum linguae. On either side is the sublingual fold 

 (Plica sublingualis) which extends from the frenum to the level of the fourth cheek 

 tooth. The fold indicates the position of the underlying sublingual gland, and 

 presents numerous small papillae, through which the ducts open. Behind the last 

 tooth a vertical fold of the mucous membrane passes from upper to lower jaw. This 

 is termed the plica pterygomandibularis ; it contains a ligament of like name. 



The isthmus faucium is the orifice of communication between the mouth and 

 the pharynx. It is bounded above by the soft palate, below by the root of the 

 tongue, and laterally by the anterior pillars of the soft palate. It is relatively 

 small and not very dilatable in the horse, and is closed by the soft palate under 

 normal conditions, except during deglutition. 



THE TONGUE 



The tongue (Lingua) is situated on the floor of the mouth, between the rami of 

 the mandible, and is supported mainly in a sort of sling formed by the mylo-hyoid 

 muscles. Its posterior part, the root (Radix linguae), is attached to the hyoid bone, 

 soft palate, and pharynx. Only the upper surface of this part is free, and slopes 

 downward and backward. The middle part, the body (Corpus linguae), has three 

 free surfaces. The dorsal surface is slightly rounded. The lateral surfaces are 

 nearly flat for the most part, but anteriorly become rounded and narrower. The 

 ventral surface is attached to the mandible. The apex or tip (Apex linguae) is 

 free, spatula-shaped, and presents upper and lower surfaces and a rounded border. 

 The term dorsmn linguae is applied to the dorsal surface; it is free throughout, 

 and in the resting state of the parts is in contact with the palate except at the glosso- 

 epiglottic space. 



Structure. — The tongue consists of: (1) The mucous- membrane; (2) the 

 glands; (3) the muscles; (4) vessels and nerves. 



The mucous membrane (Tunica mucosa linguae) adheres intimately to the 

 subjacent tissue, except on the lower part of the lateral surfaces of the body and 



